| Method for forecasting the contrast medium flow in a living body -> Monitor Keywords |
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Method for forecasting the contrast medium flow in a living bodyRelated Patent Categories: Drug, Bio-affecting And Body Treating Compositions, In Vivo Diagnosis Or In Vivo Testing, Magnetic Imaging Agent (e.g., Nmr, Mri, Mrs, Etc.)Method for forecasting the contrast medium flow in a living body description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060239918, Method for forecasting the contrast medium flow in a living body. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] The present application hereby claims priority under 35 U.S.C. .sctn.119 on German patent application number DE 10 2005 006 657.7. filed Feb. 14, 2005, the entire contents of which is hereby incorporated herein by reference. FIELD [0002] The invention generally relates to a method for forecasting the contrast medium flow in a living body, for example in a patient. In at least one embodiment, it generally relates to a method in which a defined test bolus with a contrast medium is injected, for example intravenously and with a known injection flow profile, into the body, for example into a blood vessel, the time concentration profile of the contrast medium is observed and determined over a limited time period Z with a number of measuring instants at at least one location in the body with the aid of a tomographic method. Further, the time profile of the contrast medium concentration of another contrast medium dose is forecast from the measured data obtained via the distribution of the contrast medium with the aid of a linear cause/effect formulation. BACKGROUND [0003] In tomographic methods, particularly in the field of computed tomography or NMR tomography, it is advantageous to apply contrast media in order to display specific body regions because of the low contrasts in the display that occur there, and thereby to obtain a more contrasting image of these body regions. However, contrast media mostly have the disadvantage that they are biologically incompatible and that their dose therefore has to be kept as low as possible. Because of the biological variability of the bodies under examination, however, it is impossible to make a sufficiently accurate and generally valid statement as to how the concentration profile of a specific contrast medium dose will develop over time at an observed location in the body. It is therefore necessary in the case of each body under examination to make a test injection of a contrast medium or test bolus dose so as to observe the effect thereof, in particular the subsequent time profile of the concentration values at the location of interest in the body to be examined. [0004] In the case of application in association with a CT examination, the concentration is measured indirectly over a specific time period after the test bolus injection and with the use of the smallest possible radiation doses, this being done via the changes in the HU values resulting there. Since only the imaging effect of the contrast medium is of interest, and there is a linear relationship between the imaging effect and concentration of the contrast medium, a statement on the absolute concentration of the contrast medium remains open and trivial. Again, the resolving power of the images of such a test examination remains slight. [0005] It is known to use knowledge of the effect of such a test bolus dose with the aid of a Fourier transformation as a basis for preliminary calculation of the effect of a correct contrast medium dose, and thus for determining the absolutely necessary dose of contrast medium. SUMMARY [0006] It is an object of at least one embodiment of the invention to find an improved forecasting method. As such, it can be possible to make a better forecast of the absolutely necessary contrast medium dose for examining a specific body region. [0007] The inventors have realized the following: [0008] Thus, in accordance with at least one embodiment, an aim is to find an improved method that forecasts the time profile of enhancement values at the same point using a further, different injection protocol from the time profile of the enhancement values after a test bolus injection. This is intended to serve the purpose of planning an optimal contrast medium protocol. Here, enhancement values are understood as the effects of the concentration changes of the contrast medium on the pictorial display. A CT examination is thus the HU values determined, for example. [0009] The profile of the test bolus can be represented by the following linear function: b.sub.T(t)=F.sub.T.THETA.(t-t.sub.0T).THETA.(t.sub.FT-t) (1) F.sub.T representing the flow rate, t.sub.0T the starting time and t.sub.FT the end time of the test bolus b.sub.T(t). Here, .THETA.(t) designates the Heaviside or so-called step function, that is defined as follows: .THETA. .function. ( t ) = { 1 for t > 0 0 for t < 0 . ( 2 ) [0010] The quantity of contrast medium consumed is then yielded as F.sub.T(t.sub.FT-t.sub.0T). The profile of the enhancement values c.sub.T(t) at the prescribed point owing to the dose of a test bolus is given by c.sub.T(t)=c.sub.0+{tilde over (c)}.sub.T(t) (3) in the case of a CT examination the HU value without a contrast medium dose being designated by c.sub.0, and {tilde over (c)}.sub.T(t) being the component caused by the contrast medium. These data can now be used to forecast the profile of the enhancement values c.sub.R(t) for providing a dose of a correct bolus, that is to, say one used for the examination, at the same point c.sub.R(t)=c.sub.0+{tilde over (c)}.sub.R(t), (4) when an altered contrast medium bolus b.sub.R(t) with b.sub.R(t)=F.sub.R.THETA.(t-t.sub.0R).THETA.(t.sub.FR-t), (5) is applied or injected. [0011] It is known to deduce the correct bolus dose, and the contrast medium concentration resulting therefrom, by simply adding up the measured test bolus curve in a way offset according to the lengthened bolus injection time. At least one embodiment of this method certainly functions very reliably, but it has the disadvantage that the duration of the contrast medium flow is limited to integral multiples of the duration of the test bolus. [0012] It is likewise known to apply a Fourier transformation of the measured test bolus curve in order to deduce the effect of the correct bolus dose. By diverting via the Fourier transform of the test bolus curve, it is possible to circumvent the limitation of the duration to integral multiples of the duration of the test bolus. Since, however, the test bolus curve generally comprises a few, very noisy data points, the calculation of the Fourier transform is numerically extremely unstable and thus unsuitable for data that are recorded in everyday clinical practice. [0013] Moreover, the problems arise with these methods when the test bolus data do not embrace the entire enhancement curve, that is to say have been scanned too early or too late. Since, in addition, the recirculation of the contrast medium plays an important role for a stable forecast, there would actually be a need to make a very long measurement of the test bolus for the methods. [0014] According to at least one embodiment of the invention, at least one of these problems may be lessened or even avoided as follows by way of a different calculation method that is based on a linear cause/effect relationship. In addition, a physiological model can be used for forecasting for examination time periods not measured during the test run. [0015] Forecasting by using a simple linear formulation: [0016] An essential assumption of this method of at least one embodiment, is the linearity between cause (=contrast medium dose) and effect (=the increase in the HU values in the case of the CT examination). This assumption may be expressed mathematically by the following relationship {tilde over (c)}(t)=.intg..sub.-.infin..sup..infin.dt'k(t-t')b(t'), (6) b designating bolus curves below, and c contrast medium curves. Here, k is an arbitrary patient-specific function and describes the response of the respective body to the injection of the contrast medium. [0017] A consideration of the Fourier transformation of this equation yields. {tilde over (C)}(.xi.)=K(.xi.)B(.xi.), (7) the Fourier transform of a function f(t) being given here by F(.xi.)=.intg..sub.-.infin..sup..infin.dtf(t)exp(i.xi.t). (8) [0018] The relationship (7) holds both for the test bolus and for the bolus to be forecast. The test bolus is used in order to determine K(.xi.), .xi. being the variable in Fourier space corresponding to time K .function. ( .xi. ) = C ~ T .function. ( .xi. ) B T .function. ( .xi. ) , ( 9 ) so that then {tilde over (c)}.sub. (.xi.), the Fourier transform of the concentration profile, can be determined with the aid of the following formula C ~ R .function. ( .xi. ) = B R .function. ( .xi. ) B T .function. ( .xi. ) .times. C ~ T .function. ( .xi. ) . ( 10 ) [0019] The function {tilde over (c)}.sub.R(.xi.) being sought then results therefrom by way of the inverse Fourier transformation f .function. ( t ) = 1 2 .times. .pi. .times. .intg. - .infin. .infin. .times. d .xi. .times. .times. F .function. ( .xi. ) .times. exp .function. ( - I.xi. .times. .times. t ) ( 11 ) [0020] This procedure is used in general in order to determine the contrast medium profile via a Fourier transformation. Since the Fourier transform of the test bolus is known, however, it is thereby possible to forecast the contrast medium profile for an arbitrary, different rectangle of a bolus injection, but also for entirely arbitrary contrast medium injections. Here, "rectangle" is to be understood as a constant flow of contrast medium during the injection over a specific time that is represented as a rectangle when plotted graphically and in an idealized fashion. The detailed derivation follows for an arbitrary different rectangle, and the end result for arbitrary injection curves. [0021] The Fourier transformation of the two boli (1) and (5) is given by B I .function. ( .xi. ) = F I .times. 1 I.xi. .times. ( exp .function. ( I.xi. .times. .times. t FI ) - exp .function. ( I.xi. .times. .times. t 0 .times. I ) ) , ( 12 ) so that the Fourier transform of the enhancement curve being sought results as C ~ R .function. ( .xi. ) = F R .times. exp .function. ( I.xi. .times. .times. t FR ) - exp .function. ( I.xi. .times. .times. t 0 .times. R ) F T .times. exp .function. ( I.xi. .times. .times. t FT ) - exp .function. ( I.xi. .times. .times. t 0 .times. T ) .times. C ~ T .function. ( .xi. ) . ( 13 ) Continue reading about Method for forecasting the contrast medium flow in a living body... Full patent description for Method for forecasting the contrast medium flow in a living body Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Method for forecasting the contrast medium flow in a living body patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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